The present invention relates to a shift arrangement for a motor vehicle gearbox, having a shift element which can be connected or is connected to a shift member such as a shift fork, having a hydraulic actuator by means of which the shift element can be moved in a first shifting direction and in an opposing second shifting direction, wherein the hydraulic actuator comprises a double-acting hydraulic cylinder which has a first cylinder port and a second cylinder port, and having a hydraulic circuit which has a pump and which is connected to the first and second cylinder ports, wherein the pump is connected to a pump drive.
Such a shift arrangement can be used, in particular, for the automated activation of shift clutches, such as can be used in motor vehicle gearboxes which are constructed according to the lay shaft principle. The shift clutches are preferably constructed here as synchronous shift clutches, and as a rule in each case two synchronous shift clutches are combined to form one shift clutch packet such that the two shift clutches can be opened and closed by means of a shift member such as a shift fork, in order to engage and disengage gear speed stages of the motor vehicle gearbox.
In the case of manual shift gearboxes, the shift clutches are activated by a driver with muscle force. In automated forms of such motor vehicle gearboxes such as, for example, automatically controlled transmissions (ACT), double clutch transmissions (DCT) and the like, the shift clutches are activated by extraneous force by means of actuators. The actuators can operate according to electrical, hydraulic and pneumatic active principles.
In motor vehicle transmissions such as are used, in particular, in passenger cars, in particular hydraulic actuators and electric motor actuators as well as combinations thereof are used.
Electric motor actuators are frequently used in combination with shift drums. However, these have basically the disadvantage of purely sequential activation.
Furthermore it is known to provide for each shift clutch packet, a shift rod which is activated by means of an associated actuator, in particular by means of a double-acting hydraulic cylinder. In such hydraulic actuators, generally a pump is provided which is frequently driven via the drive motor (internal combustion engine) and generates a line pressure on its pressure side. Line pressure is adjusted by means of a pressure control valve which is actuated electromagnetically. Such valves require a high degree of cleanliness during the fabrication and during the mounting of such hydraulic circuits. The necessary actuating pressures for the hydraulic actuators are likewise typically generated here by means of electromagnetically actuated valves which are generally embodied as directional control valves.
Because the pump is coupled to the drive motor, a relatively large requirement of auxiliary energy occurs continuously during operation of the vehicle, while electromechanical actuators generally only require auxiliary energy when a shift process is to be actually carried out.
In addition, in such systems the engagement and disengagement of gear speeds is generally possible only when the drive motor is running, with the result that in modern drive concepts (hybrid drives) restrictions arise with respect to the functionality. However, electromechanical actuators are generally very large in size and become geometrically awkward in shape owing to the necessary ratio gearboxes (gear mechanisms) and the transmission mechanics (shift drum). It is therefore difficult to arrange such electromechanical actuators in a gear mechanism package. In particular in the case of longitudinal in-line drive trains, the use of such actuators is frequently not possible owing to the narrow spatial conditions.
Instead of the above-mentioned shift rods, which are each assigned to a shift clutch packet, shift arrangements are also known which use one or more shift shafts. Such shift shafts can be moved both in a shifting direction and in a selecting direction. In the case of a movement in a selecting direction, in each case a shift packet is selected, for example by means of shift fingers on the shift shaft. Document DE 10 2004 052 804 B3 discloses a shift arrangement for an automated multi-step gearbox which has two shift shafts. Each of the shift shafts can be moved in a shifting direction (longitudinal direction), by means of an associated, double-acting hydraulic cylinder. In addition, an electric motor for rotating the shift shaft in the selecting direction is provided for each shift shaft. In addition, this document is concerned with mechanical locking devices which, are, however, not a subject matter of the present application.
Document DE 10 2008 031 815 A1 discloses a further shift arrangement which has a shift shaft on which a multiplicity of driver fingers are arranged for each shift clutch packet, with the result that it is possible to couple the respective shift member and the shift shaft in a multiplicity of relative axial positions with respect to one another. In this shift arrangement, a separate electric motor is respectively provided for the movement of the shift shaft in the shifting direction and for the movement of the shift shaft in the selecting direction.